1. Field of the Invention
The present invention relates to a variable displacement swash plate compressor which is particularly suitable as a refrigerant compressor for an automotive air-conditioning apparatus.
2. Description of the Invention
A swash plate refrigerant compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system is disclosed in U.S. Pat. No. 4,963,074. As disclosed therein, a swash plate is supported on a rotatable shaft of the compressor so that a change in inclination angle or tilt of the slant plate causes the reciprocating stroke or stroke length of each piston to change. The swash plate is connected with a rotor plate rotatably supported on the rotatable shaft through a single hinge coupling mechanism so that the swash plate and rotor plate rotate in unison.
The hinge coupling mechanism includes a first arm portion projecting axially from an outside surface of the rotor plate and a second arm portion projecting from the swash plate toward the first arm portion. The first and second arm portions overlap each other and are connected to one another by a guide pin which extends into a rectangular shaped hole or slot formed through the first arm portion and a pin hole formed through the second arm portion. Referring to FIG. 4, a hinge coupling mechanism of the above type is illustrated in cross section. As shown therein, the first arm portion and second arm portion are slidably connected with one guide pin and one snap pin through the rectangular hole. In the above compressor, this hinge coupling mechanism is the only hinge coupling mechanism included.
Referring to FIG. 5, the reaction force Fp of a piston in its gas compression state in a cylinder is illustrated as acting against the swash plate and is finally received by the hinge coupling mechanism. Moment Mp is indicated as the product of reaction force Fp and length Lp which is the distance between the ends of the swash plate. The axial force Fh acting on the hinge mechanism is a function of moment Mp since this moment is equal to the moment formed by Fh and the distance Lh between the hinge mechanism and the center of the swash plate. The following equations illustrate the relationship: EQU Mp=Fp.multidot.Lp EQU Fh.multidot.Lh=Mp EQU Fh=Lp/Lh.multidot.Fp
Thus, the magnitude of force Fh is large compared with force Fp since length Lb is small compared with length Lp.
One of the disadvantages of the above compressor is that a large axial force acts on the single hinge coupling mechanism causing excessive wear between the outer peripheral surface of the guide pin and the surface of a rectangular shaped hole or slot of the rotor plate. As a result of this wear and deterioration of the hinge coupling mechanism, capacity control of the compressor is adversely affected and adjustment of piston stroke by adjustment of the angle of inclination or tilt of the swash plate to vary compressor capacity cannot be reliably achieved.